Acoustic sensors are used in numerous applications to detect and monitor acoustic disturbances in transmissive media. For example, given the good acoustic transmission characteristics of water, hydrophones allow the subsurface activity of a variety of subjects including marine mammals and submarines to be conveniently monitored. Similarly, microphones are commonly used to convert acoustic transmissions through air into electric signals for reproduction and analysis. When appropriately attached to a solid structure, such sensors can even be used to monitor the exposure and reaction of the structure to vibration.
In each of these applications, it may be desirable to employ an acoustic sensor exhibiting several particular characteristics. If the sensor is to respond to a broad range of acoustic transmissions, it should have a wide bandwidth. In addition, the sensor preferably will exhibit a relatively flat response to transmissions throughout its bandwidth, ensuring that transmissions of equal amplitude are interpreted equally. If the sensor is to provide accurate, easily interpreted information, it should also exhibit a relatively high signal-to-noise ratio. Further, in certain applications the sensor may be subject to conditions that require it to be relatively rugged and impervious to its environment. Finally, it would be desirable to provide an acoustic sensor that is relatively inexpensive and simple in construction.